Under certain operating conditions, mostly at or near idle engine speed, in a four cycle reciprocating marine engine, liquid water can run backward in the marine exhaust system, whereby liquid water flows backward from the exhaust system into the engine cylinders.
Specifically, the invention addresses such marine engine/exhaust assemblies wherein cooling water flows through a water jacket in the exhaust system, to quickly cool the exhaust gases soon after the exhaust gases leave the engine exhaust ports. Typically, such cooling water is directed through a water jacket on the exhaust manifold, or whatever other structure first receives the exhaust gases from the engine. After circulating through the water jacket, the cooling water is injected into the exhaust gas stream, downstream from the water jacket.
Such injected water mixes with the exhaust gases, thus to further cool the exhaust gases. The mixture of exhaust gases and water then travel together to the exit of the exhaust system. The primary reason for mixing the liquid water with the exhaust gases is to cool the exhaust gases sufficiently that rubber components of the exhaust system not be damaged by the exhaust gases.
A first source of the condensed liquid water of concern is the hot exhaust gas which comes into contact with a colder surface of the metal exhaust manifold, where the metal exhaust manifold has a temperature cold enough to condense water vapor out of the exhaust gases. Water vapor, which is a primary component of the engine exhaust gases, condenses out of the exhaust gases onto the exhaust manifold walls, flows downwardly, and accumulates on a lower surface of the exhaust manifold. In some instances, such condensation takes place downstream of the exhaust manifold, in an exhaust pipe, wherein the condensed liquid water accumulates on a lower surface of the exhaust pipe.
A second source of water accumulation on a lower surface of the exhaust manifold or exhaust pipe is based on a phenomenon known as reversion. Reversion occurs when, in operation of the intake valves and the exhaust valves, both an intake valve and an exhaust valve are momentarily open at the same time. Specifically, the engine/exhaust combination is most susceptible to reversion when a piston is positioned between near and approaching top dead center, and near and just after top dead center, during the transition from the upward exhaust cycle to the downward intake cycle. This momentary valve-timing occurrence is known as valve overlap.
When valve overlap occurs, the high negative pressure of the intake plenum can cause the direction of flow of exhaust gases in the exhaust manifold and the down stream exhaust conduit pipe to momentarily be reversed. This reverse direction of flow of exhaust gases, known as reversion, can carry with it any of the liquid cooling water which is injected into the exhaust gas stream. The reverse direction flow of exhaust gases can cause the injected liquid water to be pulled, or walked backward, into the exhaust manifold or other water-jacketed exhaust system component. After a period of operation under such reverse direction flow conditions, this water can accumulate on the floor or other lower surface of the respective exhaust system component.
When this water, either exhaust gas condensate, or reversion in injected water, or both, accumulates in quantity large enough to flow backward into an engine cylinder at the respective exhaust port, either by gravity or by further operation of reverse exhaust gas flow of the reversion process, such flow does occur, whereby the liquid water flows back into a respective cylinder.
When the liquid water, which is essentially incompressible, flows into the engine cylinder in sufficient quantity, the piston is prevented from moving through the compression stroke when the piston reduces the cylinder volume to essentially the volume of the water in the cylinder, before the piston completes the compression stroke. When that happens, the engine is stopped dead. The engine cannot turn further because completion of the compression stroke of the piston requires further reduction of the space in the cylinder, but the liquid water in the cylinder cannot compress and there is no path by which the water can quickly escape. Thus, the piston movement is blocked by the incompressible water. While the water can be removed by removing the spark plug, the only full cure for the water in the cylinder is to disassemble the engine in order to repair the damage done by the water.
Even if the quantity of water entering the engine is not great enough to stop the engine from running, such water ingestion can cause other problems. For example, any quantity of liquid water in the engine can cause corrosion. In addition, under certain conditions, the water can, over time, leak past the piston rings, and thereby enter the underlying oil reservoir, commonly known as the lubricating oil reservoir, or the oil crank case. In the crank case, the water becomes entrained with the engine lubricating oil, and is thus distributed throughout the engine as the oil is pumped through the oil passages, and onto all parts which are lubricated by the oil. The presence of the water in such loci, even though carried by oil, works to initiate corrosion in respective ones of the engine parts and areas so exposed to the water.
The resulting corrosion can occur throughout all areas, and in all parts, of the engine to which the oil flows because all the contaminated oil, which is pumped to all areas of the engine, is contaminated. The most predominant place for corrosion to occur is on the cylinder walls, which is the first area to see the ingested water. In some instances, the corrosion can become severe enough to cause engine components, which are supposed to slide with respect to each other, to freeze together. The greatest risk of corrosion, and the most rapid spread of corrosion, typically occur where the boat is being used in salt water, whereby salt water is being used as the cooling water.
The condensation portion of the above described problem occurs in all internal combustion reciprocating engines when a given engine is cold. For engines which are not used in a marine application, when the engine starts operating, the heat of the exhaust gases rapidly heats up the walls of the exhaust conduit system to the point where water vapor stops condensing, and any already-condensed water is either evaporated and carried out of the exhaust system as vapor, or the liquid water is physically entrained in the exhaust gases by the force of flow of the exhaust gases. Such non-marine engine/exhaust assemblies are so exposed to ambient air that heat build-up is of less concern, and since cooling water is not so available as in a boat, such water-jacketed exhaust systems are typically not used, whereby condensate and reversion in the exhaust system, near the engine, typically do not occur.
The phenomenon of condensed water leaving the exhaust system can be observed in colder climates in non-marine applications where, for a short period after an engine is started, water can be seen dripping out of the tailpipe of the exhaust system. The liquid water stops dripping after a short period of running time as the exhaust system heats up and maintains the exhaust gas water vapor, in the vapor state.
The problem of condensed, liquid water entering the engine block through the exhaust ports, and thereby causing engine damage or engine failure is generally confined to marine engines where cooling water is necessarily used to cool the exhaust system. Namely, fresh or salt sea water, depending on the body of water involved, is pumped through water jackets which surround the exhaust pipes which carry exhaust gases away from the engine. Typically, after the sea water traverses the water jacket, that same sea water is injected into the exhaust gas flow stream in the main exhaust-carrying conduit or chamber of the exhaust pipe. Thus, in the exhaust system, the sea water first passes through a water jacket which extends around the exhaust pipe, or through a water jacket which is associated with an exhaust manifold, or both, relatively closer to the engine, and then passes from the water jacket into the exhaust gas flow stream in the main gas flow conduit or chamber of the exhaust pipe, downstream of the water jacket end portion of the exhaust system.
Without such water cooling, both in the jacket and in the exhaust gas stream, the engine enclosing compartment would overheat to the extent of creating a fire hazard in the engine compartment. In addition, without such cooling, the ambient temperature within the engine compartment would be elevated to the point where the heated ambient air, which would be ingested into the engine, would prevent the engine from developing rated power and could result in premature engine component wear due to overheating.
The advantage obtained by using water jacket cooling at high power output becomes a disadvantage, indeed a detriment, at low power output of such engines such as when the engine is run at idle speeds; for substantial periods of time, for example to get from open water to a mooring, or from a mooring to open water.
In typical engine/exhaust assemblies, the sea water pump is operated any time the engine is running. Typically, pump speed is correlated to engine speed, such as by coupling the sea water pump to the engine crank shaft, or to a drive shaft which is connected to the engine crank shaft. The sea water pump is typically driven either directly off the crank shaft or off the xe2x80x9clower unitxe2x80x9d drive shaft. The xe2x80x9clower unitxe2x80x9d is, generally speaking, that portion of the drive system which is under water when the boat is under way.
The problem with water jacketed cooling is that, at low engine speeds, relatively lower volumes of exhaust gases are flowing through exhaust pipes which are sized and configured to handle the relatively higher volumes of high temperature exhaust gases which are generated at high power output. Thus, at low engine speeds, the gas flow rates are relatively low. In addition, the exhaust gases cool rapidly, both because of the rapid expansion in the relatively quite large exhaust pipes which are sized to handle larger gas volumes, and, because the flow of cooling water through the water jacket keeps the walls of the pipes in the exhaust system quite cool.
It is well known that exhaust gases from internal combustion engines contain large quantities of water vapor. In the cool, slow-flow conditions of the above exhaust systems at low engine speeds, and as the engine cools from e.g. a high speed run, the water vapor begins to condense inside the exhaust pipes, and the initiating locus of condensation moves progressively closer to the engine exhaust ports as the exhaust system progressively cools. As the exhaust system becomes progressively cooler, the quantity of condensed liquid water in the exhaust system increases, and the threshold location of such condensation thus moves progressively closer to the engine.
At low engine speed operation, the gas flow rate can become too slow to physically entrain and carry the water away from the engine. At the low operating temperatures present during low-speed operation, and when full rated cooling water flow is maintained in the water jacket, the temperatures on the inside surfaces of the exhaust pipes close to the engine are sufficiently cool to cause water vapor in the exhaust gases to condense on the inside surfaces of the exhaust pipes proximate the engine exhaust ports.
In most marine engines, the exhaust gases are flowing upwardly as or shortly after they exit the engine at the exhaust ports, and then flow downwardly to the exhaust tip, and typically discharge the exhaust gases under the water, thereby using the water in part as a muffler of engine sound. In some marine engines, the exhaust gases flow upwardly, and then rearwardly of the boat to a discharge in the air. In such case, it is known to inject cooling water from an exhaust system water jacket into the exhaust gas stream in order to assist in muffling the sound of the engine exhaust.
Whatever the structure of the exhaust system, the result is that eventually, over a prolonged period of idle/low speed operation, condensed water can flow by gravity downwardly toward, and into, one or more of the engine exhaust ports, and from there into the respective engine cylinders, causing the above noted engine shut-down or other engine malfunction or damage.
For a given marine engine/exhaust assembly, at some critical engine speed, which can be unique to each model of engine/exhaust assembly, or other combination of engine and exhaust, the rate of heat generation in the exhaust system in combination with the rate of flow of gases through the exhaust system, are effective to physically carry the exhaust gases away from the engine ports and past the peak vertical elevation of the exhaust pipes such that either the gas flow rate physically entrains the condensate, and carries the liquid condensate out of the exhaust system at the exhaust tip, or the heat is sufficient to prevent formation of condensate close enough to the engine to cause a problem, or to vaporize any condensate already formed.
However, that critical engine speed is typically well above idle speed. In some relatively lower performance engine/exhaust assemblies, the exhaust system components remain hot enough over prolonged, periods of operation to cause any such condensed water to re-evaporate and thus be carried out of the exhaust system.
By contrast, other engine/exhaust assemblies, especially high performance engine/exhaust assemblies, do not so avoid ongoing presence of condensed liquid water, whereby the invention herein can be employed for the benefit of such engines.
Thus, it is an object of the invention to provide a control system, for marine exhaust systems, which limits accumulation of liquid water in the exhaust system, near the engine, to no more than amounts which are consistent with continued effective operation of both the engine and the exhaust system.
It is another object of the invention to provide a marine exhaust system having a control system which limits accumulation of liquid water in the exhaust system, near the engine, to no more than amounts which are consistent with continued effective operation of both the engine and the exhaust system.
It is yet another object of the invention to provide a marine drive assembly, including engine and exhaust, having a control system which limits accumulation of liquid water in the exhaust system, near the engine, to no more than amounts which are consistent with continued effective operation of both the engine and the exhaust system.
Still another object of the invention is to provide a method of limiting accumulation of liquid water in one or more exhaust chambers of an associated exhaust system, by controlling flow of cooling water in the exhaust system sufficient to maintain temperatures in the exhaust system at such levels as to limit accumulation of liquid water in one or more exhaust chambers of the exhaust system, proximate exhaust gas discharge ports of the engine, to no more than amounts of liquid water which are consistent with continued effective operation of both the internal combustion engine and the exhaust system.
In the invention, the flow of cooling sea water to exhaust system water jackets is temporarily eliminated, reduced, or otherwise restricted, under operating conditions where continuous flow of the sea water through the water jackets at rated speed-related flow rates, can run elevated risk of developing undesired levels of liquid water close to the engine. The method of accomplishing the above control of water flow is to turn on or off a sea water pump, either by turning on or off the power to the pump, or by engaging and disengaging a clutch connected to the sea water pump.
Alternatively, a flow control valve in the sea water line can be opened and closed, or modulated, to restrict or stop flow of cooling water to the exhaust system. Still another alternative is to operate a diverter valve in the sea water line, opening and closing the valve, or modulating water flow rate through the valve, to divert cooling water away from the exhaust system. The rate of flow of sea water to the exhaust system can, in the alternative, be restricted or modulated by other means such as by modulating output of the sea water pump.
Thus, the invention comprehends a family of embodiments comprising a control system for use in a marine exhaust system, a corresponding marine exhaust system, and a respective marine drive unit. The marine exhaust system is adapted for connection to an internal combustion marines engine at an inlet end of the marine exhaust system. The internal combustion marine engine has one or more exhaust gas discharge ports. The marine exhaust system comprises one or more exhaust chambers which define an exhaust gas discharge path for conveying exhaust gases from the one or more exhaust gas discharge ports of the internal combustion marine engine to an exit end of the exhaust gas discharge path. The marine exhaust system is designed to use flowing cooling water to control temperatures in the exhaust system, along the exhaust gas discharge path. The control system comprises sensing apparatus sensing at least one parameter. The at least one parameter is related to accumulation of liquid water in the one or more exhaust chambers proximate the inlet end of the marine exhaust system. The control system further comprises an electronic controller receiving, from the sensing apparatus, a signal representing the at least one sensed parameter and, in response to the signal representing a value of the at least one parameter indicating propensity for, or actual, accumulation of liquid water in the one or more exhaust chambers, proximate the inlet end of the marine exhaust system, generating a control signal. Yet further, the control system comprises water flow control apparatus receiving the control signal from the electronic controller and controlling flow of cooling water in the marine exhaust system, sufficient to maintain temperatures, in the marine exhaust system, at such levels as to limit accumulation of liquid water in the one or more exhaust chambers and proximate the exhaust gas discharge ports, to no more than amounts which are consistent with continued effective operation of both the internal combustion marine engine and the marine exhaust system.
In preferred embodiments, the sensing apparatus is selected from the group consisting of an engine speed sensor, a throttle setting sensor, an engine temperature sensor, a heat exchanger sea water temperature sensor, an engine sea water temperature sensor, an engine coolant temperature sensor, an exhaust gas flow rate sensor, an exhaust manifold temperature sensor, a manifold pipe temperature sensor, and an exhaust water jacket temperature sensor.
In some embodiments, the electronic controller comprises an engine electronic control module adapted to control general operation of a respective such marine engine.
In some embodiments, the electronic controller comprises a control module separate and distinct from any electronic engine control module.
In some embodiments, the water flow control apparatus comprises an on/off clutch.
In some embodiments, the water flow control apparatus comprises a variable speed clutch.
In some embodiments, the water flow control apparatus comprises a variable speed sea water pump.
In some embodiments, the water flow control apparatus comprises an on/off valve adapted for use between the engine and the exhaust intake, optionally comprising a diversion line out of said on/off valve.
In some embodiments, the water flow control apparatus comprises a modulating valve adapted for use between the engine and the exhaust system, optionally further comprising a diversion line out of the modulating valve.
In some embodiments, the water flow control apparatus comprises a flow-controlling clutch on the engine, and one or more flow diverter valves between the engine and the exhaust system.
Some embodiments include control structure, optionally included, or not, in the electronic controller, optionally a timer, or not, providing a pre-determined minimum flow of cooling water to the exhaust system, and overriding all other commands of the control system after activation of the control system.
In some embodiments, the water flow control apparatus further comprises a database representing modeling one or more of engine speed, exhaust temperature, and cooling water flow rate in a given combination of the engine and the exhaust system.
In a second family of embodiments, the invention comprehends a method of of limiting accumulation of liquid water in the one or more exhaust chambers proximate the exhaust gas discharge ports of an internal combustion marine engine. The exhaust system is connected to an internal combustion marine engine at an inlet end of the exhaust system. The internal combustion engine has one or more exhaust gas discharge ports. The exhaust system comprises one or more exhaust chambers which define an exhaust gas discharge path for conveying exhaust gases from the one or more exhaust gas discharge ports of the engine to an exit end of the exhaust gas discharge path. The exhaust system is designed to use flowing cooling water to control temperatures in the exhaust system, along the exhaust gas discharge path.
The method, comprises activating a control system which activates sensing of at least one parameter using sensor apparatus, the at least one parameter being related to accumulation of liquid water in the one or more exhaust chambers proximate the inlet end of the marine exhaust system. The method further comprises sending a signal from the sensor apparatus to an electronic controller; using the controller, and in response to the signal from the sensing apparatus indicating propensity for, or actual, accumulation of liquid water in such one or more exhaust chambers proximate the inlet end of the exhaust system, generating a control signal; and responsive to the control signal, controlling flow of cooling water in the exhaust system, sufficient to maintain temperatures in the exhaust system at such levels as to limit accumulation of liquid water in the one or more exhaust chambers and proximate such exhaust gas discharge ports, to no more than amounts which are consistent with continued effective operation of both the marine engine and the marine exhaust system.
In preferred embodiments, the method comprises sensing of at least one parameter selected from the group consisting of engine speed, throttle setting, engine temperature, heat exchanger sea water temperature, engine sea water temperature, engine coolant temperature, exhaust gas flow rate, exhaust manifolds temperature, manifold pipe temperature, and exhaust water jacket temperature.
In some embodiments, the method further comprises controlling flow of cooling water only when engine speed is at or below a critical upper threshhold engine speed.
In some embodiments, the method further comprises controlling flow of cooling water only when engine speed is at or below a selected engine speed substantially below full rated power output of the respective engine.
In some embodiments, the method includes controlling flow of cooling water to the exhaust system by intermittently shutting completely off flow of cooling water to the exhaust system, and subsequently turning flow of cooling water back on, optionally by turning off, and then back on a clutch connected to a sea water pump associated with the marine engine, optionally in combination with the on/off flow of cooling water, or not, by also modulating rate of flow of cooling water when water flow is turned on, to a rate less than full rated flow.
In some embodiments, the method includes controlling flow of cooling water to the exhaust system by turning water flow off, and subsequently on, in cycles, according to a pre-set timing sequence.
In some embodiments, the method includes intermittently turning off, and subsequently back on, flow of cooling water using a valve between the engine and the exhaust system.
Some embodiments include modulating flow of cooling water to the exhaust system using a modulating valve between the engine and the exhaust system.
Some embodiments include monitoring engine speed, modulating flow of cooling water to the exhaust system above a pre-determined engine speed, and when the engine is operating below the pre-determined speed, intermittently turning off flow of cooling water and subsequently turning flow of cooling water back on, in cycles.
Some embodiments include sensing an exhaust system temperature and, irrespective of engine speed, and optionally based only on the sensed exhaust system temperature, controlling flow of cooling water to the exhaust system in accord with pre-selected trigger water temperatures or a target water temperature in combination with a temperature tolerance range.
The method preferably includes also sensing engine speed, and implementing the control of cooling water to the exhaust system only when engine speed is below a predetermined threshold engine speed.
In preferred embodiments, the method includes providing a pre-determined minimum flow of cooling water to the exhaust system, overriding all other commands of the control system any time the control system has been activated.
In some embodiments, the engine includes an electronic control module, and the method includes providing, as the controller, a system control module, separate and distinct from the engine electronic control module, the system control module communicating with the engine electronic control module.
Some embodiments of the method include modeling a combination of engine and exhaust, thereby collecting temperature response data representative of exhaust system temperature at various engine speeds, as related to time at the respective speeds, and controlling flow of cooling water to the exhaust system at least in part based on the data in the database which is representative of the respective engine and exhaust.